Method of coating sheet material with wax



Patented June 16, 1953 METHOD OF COATING SHEET wWIrH WAX [OFFICE MATERIAL George G. Runiberger, Neenah, Wis., assignorto QMarathon Corporation, Rothschild Wis., a corporation of Wisconsin No Drawing. ApplicationMarch 23,1951, 7

Q I g eri 1-No.'217,299 I e 17 an's- (01. 117- 103) This invention relates to a method of coating sheet 'materials with hotimelt coatings. ,More

specifically this invention relates to, an improvesuch as paper, paperboard, regenerated cellulose, rubber hydrochloride, polyethylene and other plastic films and the like, with hot melt surface coatings wherein the coatings are cooled under controlled conditions to prevent the formation of irregular flow lines therein, sometimes known in the art as crows feetff whereby the production of smooth, uniform and even surface coatings is insured. This application is a con tinuation inpart of my application Serial No. 784,929 filed November 8, 1947, now abandoned.

In the application of water-proof or water vapor-proof coating materials, such as wax, wax compositions and wax-like resinous coatings to sheet materials by the hot melt method, it is the practice to apply the coating composition in a molten state, and then to chill the coating rapidly in order to set the composition before it has completely penetrated the sheet material, so as to form a superficial surface coating. 'Ihe cooling operation is generally conducted either by passing'the coated sheet material overrefriger- 'ated rolls or by contacting the coated sheet material with cold 'water, such as passing it through a cold water bath. When the latter method of cooling is employed, increased rates of cooling are possible due to thefact that the coolingliquid comes into intimate contact with the surface film. substantially the same practice is followed in coating pre-cut paperboard carton; blanks where it is the practice first to apply the coating material, remove the excess, and rapidly plunge the coated blank into cold water to set the coating Processes of coating wherein the coatingmaterial is cooled by immersion in water are called water-waxing. H

It has been found, however, that when water is employed as a cooling medium fori'the immersion of the coated sheet material, as in stand-- ard commercial production, irregular fiowlines; crevices, ridges and other irregularities referredto as crows feet appear on the surface film. Due

to these irregularities in the surface the coated ment in the method of coating sheet materials,

face ,of hot melt coatings by turbulence in the cooling water. Under ordinary commercial conditions this turbulence is caused by the agitation of the coolingibath by the sheet material travel-3 ing therethrough at the high speeds required in commercial production of coated sheets, or inthe case-of carton blanks by both the high speed and the intermittent flow of material. Following this discovery I have developed a method whereby microscopic crows feet 0.1 fiow lines can be -reduced or eliminated under commercial operating conditions even at-high speeds of operation, such as at about 300 feet, per minute and above, and

particularly at speeds in the range of about 500 to about 1000 feet per minute, by adjusting the surface tension of the cooling liquid so that it approaches the surface tension of the applied coating. Crows, feet are thereby minimized or completely eliminated even though 'theicooling liquid is in a state of turbulence, Whether.result-= ing from. high speeds of operation or created by other means. Theelimination of flow lines in the coating improves the gloss and also the resistance of the coating to rub off or .scufi; Hydrocarbon waxes, such as paraffin wax,

which are; used, in coating-sheet materials have-- in general asurface'tens'ion of from about 25 'to about 29 dynes per centimeter (d./cm.) when measured at-l80 F. At higher temperatures these values would be somewhat lower. When,

waxesarecompounded with other materials for use as moisture-proof and water-vapor-proof coatings, the surface tension of .the resulting composition may be greater or less than these values, and the surface tension of the cooling liquid; should be adjusted accordingly. I have found that, in general, coating compositions suitable for this purp se have surface tensions'at the temperature of application in the range ofabout 20 t0 abou 0 will be from about 130 F. to about 300 F. The

examples of such sheets are less glossy than similar coated sheets i having a smooth coating. Furthermore, there is i a distinct tendency for a coating having these irregularities in the surface to scuff or rub ofi.

After considerable experimentation with the: 1 factorsinvolved. in the hot-melt coating of wax i compositions, specifically in water-waxing, I 1? found that crows feet are producedon the sur- 'theparaffin wax,

-modif y the'wax to make it difference between the temperature of applicaber, amides, such as stearamide or ste'aranalid, antioxidants, such as butylated hydroxy anisole or other phenols, or other materials required to suitable for the need at hand, wh1ch may modify the surface tension d-'/ In a he temp ture range at which these coatings areapplied of the composition. The hydrocarbon wax portion of the composition will, in general, be more than 50% by weight. The viscosities of these compositions at their application temperature will vary with the composition, but they do not generally exceed about 100 centistoke'sat such temperature. I have found no necessity for having the surface tension of the coolant below that of water when higher viscosity compositions are applied or, in other words, I have found that flow lines or crows feet do not occur during water-waxing with compositions having a viscosity in excess of about 100 centi'stokes at the application temperature.

For very high speed coating, or when turbulence is high in the cooling bath for other rea- 4 coolant as possible by physical means, such as scrapers, rollers, or suction tubes, then pass the sheet through a washing bath of cold water to remove the residual coolant, then remove the water by physical means.

It is obvious that coolants having an appreciable solvency for, or deleterious action on, the composition cannot be used. Therefore, I prefer to' use aqueous or alcoholic cooling solutions. For reasons of economy aqueous coolants containing alcohols are preferred. Furthermore,

aqueous solutions are less toxic and harzardous to handle.

sons, I have found that the" best results are obtained if the surface tension of the cooling liquid at its temperatureexceeds that the coating composition at the temperature it contacts the coolant by not more than about 5 d./cm. For relatively lower speeds of operation the sur-' face tension of the coolant preferably should not exceed that of the coating composition by more than about d./cm. although in cases where the viscosity of thecoating is more than about 50 centistokes at the temperature of contact this difference may be even greater. In general, any lowering of the surface tension below that of water will benefit the coating to some degree. However, for the class of compositions to which my invention isapplicable, I have found that the surface tension of the collant should in no case exceed about 60 d./cm. at its operating temperature, and for hydrocarbon wax and modified wax compositions having a viscosity of less than about 50 centistokes at the temperature of contact, the upper limit is preferablyabout 45 d./cm. I have found that if the surface tension of the coolant is in the range of about 3 to about 20 'd./cm. above that of the coating at their respectivetemperatures during coating, which may be 50 F. and 180 Erespectively, good results are obtained.

Insome casesa coolant having a surface tension equal to or lower'than the coating composition may be used. {In these cases, however, the coolant wets the coating composition to such an extent that'the coolant is subsequently difiicultto remove. When these 'coolants are used, or where complete removal of the coolant is desired, I prefer to chill the sheet sufficiently to congeal the coating, then pass the-sheet through a washing bath of Water, or other liquid of higher surface tension and having a high solvency for the first coolant, then remove the washing liquid. For example, when cooling a coating composition having a surface tension of about 28 d./cm. in a coolant having a sur- The following Table I gives results obtained when 2-pounds per ream (24x36480) opaque .sulfite .breadwrapper stock was waxed with /32 F. 'ASTM melting point paraffin wax having a surface tension of 28 d./cm. at F., the temperature of application, and cooled by immersing in various cooling liquids which were agitated by blowing a stream of air into the cooling bath with sufiicient pressure to cause turbulence.

Table I Surface Tension of Example Composition of Cooling Cooling Crows-Feet Bath Bath, Produced dJcm. at

100% Water 72 Pronounced. 20% Isopropyl alcohol; 80% 35 Very slight.

Water. 3 l. 30% Ethyl alcohol; 70% v '33 Do.

Water. 4 Water Saturated with Hep- 30 'Do.

tanol at 40 F. 5 1.8% Iso amyl alcohol; 0.2% 37 Do.

isopropyl alcohol; 98.0% Water. 6 2.7% Iso aroyl alcohol; 0.3% 36 None.

Isopropyl alcohol; 97.0% 1 Water. '7 0.1% Di octyl sodium-suite 26 Do.

succinate; 999% Water. 8 0.025%Dioctylsodiumsu1io 30 Do.

succinate, 99.975% Water. 9 001.25% D1 octyl sodium 40-45 Very slight.

sulfo succinate; 99.9875% Water. 10 0.5% Alkyl Aryl sodium sul- 32 None.

fonate; 99.5% Water.

of isopropyl alcohol in water having a surface I face tension of about 25'd./cm., Iremove as much 60 tension of 31 d./cm.

TabZe'II Waxing Conditions Properties of Waxed Paper Example TSur-Iace f I Coolant 833E315? Gloss Scufi Orows-Feet .lmm. dlcm at Percent 630 Water 72 55 Great- P I 630 AlcoholWater 31 s2 Slight- Ntiti 855 Water 72 55 Great." Pronounced. 855 Alcohol-Water 31 61 Slight-.. None. 930 Water; 72 54 Grcat.- -Pronounced. 930 AlcoholWater '31 51 Slight... None.

5 From Table II it is seen that bylowering the surface tension-to 4 d./cm. above the surface tension of the coating crows feet were eliminated over a wide range of commercial production 6 vention. 'The common wetting agents such as s'ulfonated alcohols, amines, and esters are satisfactory. Akylv aryl sodium sulfonates, alkylated sodium sulfo succinates, alkyl amine acetates,

speeds. In each case where .crows feet was 5 alkyl amines, fatty acids esters of hexitol anhyeliminated, gloss and'scuff were materially. imdrides, alkyl dimethyl-benzyl ammonium chloproved. rides, can be used. Alcohols such as ethyl, propyl, The following exa ples in Table III show the I butyl, amyl, hexyl, septyl, octyl, nonyl, and decyl effect Ofusil'lg low surface tension'coolants-to cool have been found advantageous to use in their several wax compositions having-a viscosity of 1 normal and isomeric forms, not only alone, but less than 100 centistokes at 210 F- o p s also-in combination with otherwetting agents, p y ylene (P. E.)- of 7000 molecul r W ig t, where they act to suppress foam in addition to P fi WaX d o ystflline (micro) wax lowering the surface tension. I prefer, however, when coated at atemperature of about 1'75 F. 011' to use a wetting agent-which has little tendency commercial equipment at highspeeds. 5 to foam, inasmuch as foam in the cooling bath TabZe'III y TSurface f l sur face f 611Sl011 0 81181011 0 1 emporium r iiiii. $735 3, gf f %fi; 2 35? 1333a 50F. at 175 F.

17 5% polyethylene; 145/47 F. microwax; 70% 700 70 28-29 heavy.-. 67 130/ F. paraffin wax. 18 Same as 17 780 40 28-29- veryiew. 73 19 2.5% polyethylene; 5.0% ISO/85 F. microwax; i 640 33 none... 76-

25.0% 145/47 F. microwax; 67.5% l30l32 F. paraffin wax. 20 Same as l9. 550 72 30 few 75 21 d0 550 34.5 30 none 82 Examples 18, 19 and 21 clearly show an improved 3o lowers its cooling efficiency. I have found that result where .the surface tension of the coolant when foam suppressers, such as, the silicones and has been lowered to .providea difference in surhigh molecular weight alcohols, e. g., octyl and face tension between the composition and the nonyl alcohol, are used with foaming types of coolant of not more than 20 and particularly in wetting agents good results can be'obtained the range of about 3 to 5. Examples 17 and 20 In thepractice of my invention I prefer to use illustrate the fact that there is a greater tendalcohol-water solutions, inasmuch as these soluency for crows feet to form' at higher speeds. tions do not foam. In addition they are prefer- Example 18 illustrates that at thes high speeds able since the solubility of air in such mixtures is a difference of surface tension of about 10 does quite low. Furthermore, alcoholic solutions can not completely eliminate crows feet. As stated 4 be cooled to very low temperatures without freezabove we preferably would employ a difference of ing or separation of the constituents. not more than 5. It is to be understood that the specific examples Table IV illustrates still other compositions apgiven are intended as illustrative embodiments plied at 210 F. thatI have found to be beneof the present invention and that numerous fitted by cooling in aqueous cooling" baths having changes and modifications of the factors of the a surface tension lower than God/cm. at 50 F. resent invention are feasible which are intended Table IV Surface Approximate surtension of Viscosity face tension of Ex. Composition Composienticoolant at 50F,

tion,d./cm. stockes at above which at 210 14 210 F. crows-feet appear 9 9% polyethylene; 40% 145/47 F. microwax; 61% 27 24. 0 43 d./cm.

l35/37 F. paraflin wax, s 23 130/32 F. parafin wax; 50% 170/75 F. micro- 25. 6 7. 4 32-35 d./cm. 24 .l z i polyisobutylene; 97.5% l35/37 F. paraffin? 24.8 3 j 57 about d./c1n.

wax.

As previously mentioned, the lowering of-surto be included within the scope of the appended face tension of the coolant below that of water, 60 claims and more particularly below 60 d./cm., at the I claim: operating temperature, becomes unnecessary l. The process of forming on a flexible celluwhen the viscosity of the coating material rises losic sheet material a substantially smooth, uniabove about 100 centistokes at the application form and even congealed coating substantially temperature. This limitation appears to apply free of irregular flow lines which comprises apat all speeds I have been able to obtain up to plying uniformly to the sheet material a molten about 1000 feet per minute. When sheet speeds composition consisting essentially of a molten are not in excess of about 300 feet per minute, h d arb a having a surface tension of flow lines 10 not pp atany viscosity dOW about 25 to about 29 dynes per centimeter at to about 4 centistokes at temperature of applica- 130 and viscosity t exceeding 100 centp tion. Furthermore, there seems to be aviscositytoke at the temperature of application, and surface tension relatio s p f each passing said coated sheet at a high speed through I have found that any substance added to the an aqueous cooling t maintained t a t cooling bath which will lower the surface tension perature ubstantially below th melting point of sufficiently is suitable for the practice of this inthe said'molten composition, said cooling bath containing a wetting agent, said bath having a;

surface tension exceeding the surface tension of the said molten coating composition by about 3 to about 20 dynes per centimeter at-the moment of contact of the two.

2. The process of forming on a flexible cellulosic sheet material a substantially smooth, uniform and even congealed coating substantially free of irregular flow lines which comprises applying uniformly to the sheet material a molten coating composition comprising a molten hydrocarbon wax and a wax modifier, said compositions having a surface .tension of about 20 .to about 40 dynes per centimeter at the temperature of application of the coating, and passing said coated sheet at a high speed through an aqueous cooling bath maintained at a temperature substantially below the melting point of the said molten composition, said cooling bath containing a wetting agent, said bath having a surface tension exceeding the surface tension of the said molten coating composition by about 3 to about 20 dynes per centimeter at the moment of contact of the two.

3. The process of forming on a flexible cellulosic sheet material a substantially smooth, uniform and even congealed coating substantially free of irregular flow lines which comprises applying uniformly to the sheet material a'molten composition having a viscosity of less than 100 centistokes at 210 F. comprising paraflin wax, microcrystalline wax, and. polyethylene, and having a surface tension of about 20 to about 40 dynes per centimeter at the temperature of application of the coating and passing said coated. sheet at a high speed through cooling bath maintained at a temperature substantially below the melting point of the said molten composition, said bath having a surface tension at its said temperature of from about 26 dynes to about 45 dynes per centimeter at the moment of contact of said coated sheet.

4. The process of forming on a flexible cellulosic sheet material a substantially smooth, uniform and even congealed coating substantially free of irregular flow lines which comprises applying uniformly to the sheet material a molten composition comprising a molten hydrocarbon wax having a surface tension of about 20 to about 40 dynes per centimeter at the temperature of application of the coating, and passing said coated sheet at a high speed through an aqueous cooling bath maintained at a temperature substantially below the melting point of the said molten composition, said cooling bath containing a wetting agent, said bath having a surface tension exceeding the surface tension of the said molten coating composition by about 3 to about 20 dynes per centimeter at the moment of contact of the two.

5. The process defined in claim 4 wherein the wetting agent is a monohydric alcohol.

6. The process defined inclaim 4 wherein the wettingagent is isopropyl alcohol.

'7. The process defined in claim 4 wherein the wetting agent is ethyl alcohol.

8, The process defined in claim 4 wherein the wetting agent is a mixture of alcohols.

9. The process defined in claim 4 wherein the wetting agent is alkyl aryl sodium sulfonate.

10. The process defined in claim 4 wherein the hydrocarbon wax is paraffin wax.

11. The process of forming on a flexible sheet material a substantially smooth, uniform and even congealed moisture-proof coating substan tially free of irregular flow lines which comprises applying uniformly to the sheet material a molten hot melt hydrocarbon wax moisture-proof composition having a surface tension of about 20 to about 40 dynes per centimeter and a viscosity of not more than about centistokes at temperature of application, and passing said coated sheet at a high speed through a cooling bath maintained at a temperature substantially below the melting point of the said molten composition, said bath having a surface tension exceeding the surface tension of the said molten wax by not more than about 3 to 20 dynes per centimeter at the said temperature of the cooling bath.

12. The process of forming on a flexible sheet material a substantially smooth, uniform and even congealed moisture-proof coating substantially free of irregular flow lines which comprises applying uniformly to the sheet material a molten hot melt hydrocarbon wax composition having a surface tension in the range of about 20 to about 40 dynes per centimeter at temperature of application, and passing said coated sheet at a high speed through a cooling bath maintained at a temperature substantially below the melting point of said composition, said bath having a surface tension at the said temperature of the bath exceeding the surface tension of the said molten coating composition by not more than 20 dynes per centimeter.

material a substantially smooth, uniform and,

even moisture-proof congealed coating substantially free of irregular flow lines which comprises applying uniformly to thesheet material a molten hot melt composition comprising a molten hydrocarbon wax having a viscosity of less than about 100 centistokes at temperature of application, and passing said coated sheet through an aqueous cooling bath maintained at a temperature substantially below the melting point of the said molten composition, said cooling bath containing a wetting agent, said bath having a surface tension at temperature of the bath of not more than 60 dynes per centimeter and exceeding the surface tension of the said molten coating composition at the temperature at which it contacts the bath by not more than about 20 dynes per centimeter.

14. The process of forming a continuous sheet of material coated with a moisture-proof hot melt hydrocarbon wax composition having a sur-,

face tension of about 20 to about 40 dynes per centimeter and a viscosity of not more than 100 centistokes at the temperature of application comprising coating a sheet or web of a material with said composition while molten at a speed of 300 to 1,000 feet per minute and quenching the coated material in an aqueous cooling medium which will not dissolve said composition and which has a surface tension in excess from about 3 to about 20 dynes per centimeter of the sur face tension of said molten thermoplastic composition under conditions of application and not more than about 60 dynes per centimeter to form a smooth, uniform and even congealed coating 'wax composition having a viscosity of not more than 50 centistokes and a surface tension of about 20 to about 40 dynes per centimeter and comprising coating a sheet or web of a material with said composition while molten at a speed of 300 to 1,000 feet per minute and quenching the coated material in an aqueous cooling medium which will not dissolve said composition and which has a surface tension of not more than about 45 dynes per centimeter butgreater than the surface tension of said wax composition under conditions of application, to form a smooth, uniform and'even congealed coating on said web substantially free of irregular flow lines. s

16. In the method of coating sheets with hot melt hydrocarbon wax moisture-proof compositions having a surface tension of about 20 to about 40 dynes per centimeter wherein the coating is chilled by passing the coated sheet through a water bath maintained at a temperature to congealsaid coating, the improvement comprising adding a wetting agent to said water bath in sufficient amount to lower the surface tension of the bath not exceeding by about 3 to about 20 Number 6 Name Date 677,320 Norris June 25, 1901 1,140,873 6 Carter May 25, 1915 2,308,638 Balthis Jan; 19, 1943 20 2,350,742 Fordyce June 6,- 1944 dynes per centimeter the surface tension of said free of any wetting agent, and again physically removing water from said sheet.

' GEORGE R. RUMBERGER.

7 References Cited in the file of this patent UNITED STATES PATENTS 

1. THE PROCESS OF FORMING ON A FLEXIBLE CELLULOSIC SHEET MATERIAL A SUBSTANTIALLY SMOOTH, UNIFORM AND EVEN CONGEALED COATING SUBSTANTIALLY FREE OF IRREGULAR FLOW LINES WHICH COMPRISES APPLYING UNIFORMLY TO THE SHEET MATERIAL A MOLTEN COMPOSITION CONSISTING ESSENTIALLY OF A MOLTEN HYDROCARBON WAX HAVING A SURFACE TENSION OF ABOUT 25 TO ABOUT 29 DYNES PER CENTIMETER AT 180* F. AND A VISCOSITY NOT EXCEEDING 100 CENTISTOKES AT THE TEMPERATURE OF APPLICATION, AND PASSING SAID COATED SHEET AT A HIGH SPEED THROUGH AN AQUEOUS COOLING BATH MAINTAINED AT A TEMPERATURE SUBSTANTIALLY BELOW THE MELTING POINT OF THE SAID MOLTEN COMPOSITION, SAID COOLING BATH CONTAINING A WETTING AGENT, SAID BATH HAVING A SURFACE TENSION EXCEEDING THE SURFACE TENSION OF THE SAID MOLTEN COATING COMPOSITION BY ABOUT 3 TO ABOUT 20 DYNES PER CENTIMETER AT THE MOMENT OF CONTACT OF THE TWO. 